SECTION B 9 (a) What is meant by the term herbicides? chemicals used to kill weeds/inhibit weed growth; [1] (b)Outline the difference between selective herbicides and non selective herbicides giving appropriate examples if each Selective herbicides Kill certain weeds/plants Used as post emergent Absorbed by foliage/roots and translocated to other parts of the plant Dalapon/2, 4 D/ Simazine/atrazine; glyphosate/ other named appropriate selective herbicides Non selective herbicides Kill all weeds/plants; Used as pre emergent ; Absorbed by living tissues on a plant and they do not move throughout the plant tissues; Paraquat/bromaci/atrazine/simazine/other named appropriate non selective herbicides [4] (c)Outline the advantages of using herbicides over the other available methods of weed control quick/fast ; effective in controlling weeds within the rows; can be used even before the weeds set/ appear; can be used in areas where other methods are practically impossible ; conserves soil moisture by minimizing soil tillage ; guarantees almost complete control ; maintains good soil structure by minimizing soil tillage; [max 5] 10 (a) What is meant by the term plant disease? harmful/deviant condition caused by plant pathogens/deviation from normal functioning of a plant ; [1] (b)Describe the mode of infection for each of the following groups of diseases: (i)bacterial disease bacteria may be carried by wind/irrigation water/insects/crop residues/ implements/tools/soil ; enters plants wounds/cuts; [2] (ii)fungal disease spores may be carried by winds/irrigation water/insects/on seeds/crop residues/implements/tools; spores germinates when landing on wet leaves; young fungi enters healthy plants through the stomata; [max 2] (iii)viral disease viruses is carried by sap – sucking leaf hoppers/insects; the virus is injected/released into a sap of a healthy plant when the insect/sap sucking leafhopper sucks the sap/AW; [2] c)Outline necessary precautions taken to ensure safe and effective use of chemicals in the control of plant diseases application at recommended rate; wear protective clothing; read/follow instructions; spraying in calm weather/avoid spraying when it is windy/rainy; alert your neighbours of your intentions to spray; avoid eating/smoking/drinking while handling chemicals; wash hands thoroughly /with detergent after using chemicals; do not allow anybody to enters sprayed area until the required period expires; [max 3] 11 (a) outline reasons for stumping in a field to facilitate tillage operations/enables movement of machinery; to control pests/diseases; prevents competition for space/nutrients/ sunlight/water; to prevent damage to implements/tools/machines; to create space for crops/plants; to prevent injury/injury to farmers/animals; [max 4] (b)Explain how the following tillage operations contribute to soil preparation: (i)ploughing loosens the soil improving aeration/ infiltration/ drainage/ root development; inverts the soil which buries organic matter/ weeds/ unwanted material/ expose pests/pathogens; break hard pans improving aeration/infiltration/drainage/ water holding capacity ; [max 2] (ii) discing cuts surface trash hence killing weeds; breaks surface crusts improving drainage/aeration ; breaks big soil clods to cover seeds/level the soil/produce medium tilth; [max 2] (iii)harrowing breaks clots producing fine/suitable tilth; levels the soil producing uniform depth of planting/ uniform water distribution [2] 12 (a)Describe how plants leaves manufacture food have chloroplasts where photosynthesis takes place; chlorophyll/green pigment absorbs light/energy from sunlight; light/sunlight /sunlight energy splits water molecules into hydrogen and oxygen atoms; carbon dioxide is absorbed through the stomata of the leaves; carbon dioxide diffuses from the air spaces of the leaf into the cytoplasm; water passes from the xylem tissues into the cells; carbon doxide combines with water to form carbohydrates and oxygen/hydrogen combines with carbon dioxide to produce carbohydrates/ correct word equation/ balanced chemical equation ; oxygen is released as a byproduct; [max 5] (b)Outline how food manufactured in plant leaves is utilized used for plant growth/development/replacement of worn out tissues/maintenance; used for reproduction/ formation of flowers/fruits/seeds; improve quality of fruits; seeds/fruit ripening; used for seed germination; essential to drive metabolic process/respiration; essential for nutrient absorption/active transport; develop plant resistance against pests/diseases; stored for future use; [max 5] 13 Paddocks can be become dominated by less palatable and low producing pasture plants (a) Outline factors that might cause the development of less palatable and low producing pasture plants selective grazing; uncontrolled burning/veld fires; continuous grazing/not having enough rest periods; overstocking/overgrazing; failure to control weeds/bush encroachment; drought/periodic droughts; uneven distribution of water points/ poor water reticulation /use of the same pathways; mismatch between livestock type and available forage/AW; [max 5] (b)State what can be done to improve the condition of the pasture apply non selective grazing/control selective grazing; give the camp ample opportunity to rest; apply fertilizers; irrigation; put enough livestock on the land/balance stocking rate with carrying capacity/ practice correct stocking rate; reseeding with desirable species; practice supplementary feeding; match livestock type with available forage; practice rotational grazing; distribution of watering points; controlled burning; [max 5] 14. Explain each of the following economic concepts using relevant illustrations : (a) the law of demand The higher the price of a commodity, the lower the demand/ AW; [1] Price 60 Quantity 250 40 20 500 1000 Correct sketch of demand curve/demand schedule; Correct labeling of Y – axis/ column 1; Correct labeling of X-axis/ column 2; [max 2 ] Correct interpretation of law of demand/when the price of oranges per bag increased from P1/P20 to P2/P60 the quantity of oranges demanded decreased from Q1/1000 bags to Q2/250 bags/AW; [2] (b) equilibrium price Price that satisfy both the producer and consumer/price at which amount supplied is the amount demanded/AW; [1] Price 8 6 4 Demand 30 40 50 Supply 50 40 30 Correct sketch of equilibrium price; Correct labeling of supply curve and demand curve; Correct labeling of Y-axis/column 1; Correct labeling of X- axis/ column 2; Correct labeling of equilibrium price; [max 2 ] Correct interpretation of equilibrium price/ at equilibrium price P/6 the quantity of tomatoes demanded was equal to the quantity of tomatoes supplied that is 40/Quantity supplied/quantity demanded / AW; [2] 15. (a) Describe the dangers of operating a tractor without lubrication increased friction between moving parts; reduced efficiency; overheating of the engine; increased noise between moving parts/in the engine; [4] (b) Outline the differences and similarities between the mode of operation of a 4-stroke petrol engine and a diesel engine Differences Phases Petrol Diesel Induction Fuel-air mixture drawn into the cylinder Only air is drawn into cylinder Compression Fuel-air mixture is compressed Air is compressed Power Electric spark ignites fuel mixture Hot air/compressed air ignites the fuel/diesel [3] Similarities Stage Petrol Diesel Exhaust Burnt gases are swept out through the exhaust port Burnt gases are swept out through the exhaust valve Inlet valve closed and exhaust valve open Inlet valve open and exhaust valve open Piston moves up Piston moves up Inlet valve open and exhaust valve closed Inlet valve open and exhaust valve closed Piston moves down Piston moves down Both inlet and exhaust valves closed Both inlet and exhaust valves closed Piston moves up Piston moves up Both inlet and exhaust valves closed Both inlet and exhaust valves closed Piston moves down Piston moves down Induction Compression Power [3]
